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Active magnetic bearings

Active magnetic bearings (AMP)
(produced by S2M Société de Mécanique Magnétique SA, 2, rue des Champs, F-27950 St. Marcel, France)

The main areas of application of active magnetic bearings are as part of turbomachines. The concept of no oil in compressors and turboexpanders makes it possible to achieve the highest reliability also due to the absence of wear on machine components. Active magnetic bearings (AMP) find everything greater application in many industries. To improve dynamic characteristics, increase reliability and efficiency, non-contact active magnetic bearings are used.

The operating principle of magnetic bearings is based on the effect of levitation in a magnetic field. The shaft in such bearings is literally words hanging in a powerful magnetic field. The sensor system constantly monitors the position of the shaft and sends signals to the stator position magnets, adjusting the force of attraction on one side or another.

1 . general description AMP systems

The active magnetic suspension consists of 2 separate parts:

Bearing;

Electronic control system

The magnetic suspension consists of electromagnets (power coils 1 and 3) that attract the rotor (2).

AMP components

1. Radial bearing

The radial bearing rotor, equipped with ferromagnetic plates, is supported by magnetic fields created by electromagnets located on the stator.

The rotor is placed in a suspended state in the center, without contacting the stator. Rotor position is controlled inductive sensors. They detect any deviation from the nominal position and provide signals that control the current in the electromagnets to return the rotor to its nominal position.

4 coils placed along the axes V and W , and shifted at an angle of 45° from the axes X and Y , hold the rotor in the center of the stator. There is no contact between the rotor and stator. Radial clearance 0.5-1mm; axial clearance 0.6-1.8 mm.

2. Thrust bearing

A thrust bearing works on the same principle. Electromagnets in the form of a permanent ring are located on both sides of the thrust disc mounted on the shaft. Electromagnets are fixed to the stator. The thrust disc is mounted on the rotor (for example, using the shrink fit method). Axial position sensors are usually located at the ends of the shaft.

3. Auxiliary (insurance)

bearings

Auxiliary bearings are used to support the rotor while the machine is stopped and in the event of failure of the AMS control system. During normal operation, these bearings remain stationary. The distance between the auxiliary bearings and the rotor is usually equal to half the air gap, however, if necessary, it can be reduced. Auxiliary bearings are mainly solid lubricated ball bearings, but other types of bearings such as plain bearings can also be used.

4. Electronic control system

An electronic control system controls the position of the rotor by modulating the current that passes through the electromagnets depending on the signal values ​​of the position sensors.

5. Electronic processing system signals

The signal sent by the position sensor is compared with a reference signal, which corresponds to the nominal position of the rotor. If the reference signal is zero, the nominal position corresponds to the center of the stator. When changing the reference signal, you can move the nominal position by half the air gap. The deviation signal is proportional to the difference between the nominal position and the rotor position in this moment. This signal is transmitted to the processor, which in turn sends a correction signal to the power amplifier.

Ratio of output signal to deviation signaldetermined by the transfer function. The transfer function is selected to maintain the rotor as accurately as possible in its nominal position and to return it quickly and smoothly to this position in the event of disturbances. The transfer function determines stiffness and damping magnetic suspension.

6. Power amplifier

This device supplies the bearing electromagnets with the current necessary to create magnetic field, which acts on the rotor. The power of the amplifiers depends on the maximum strength of the electromagnet, the air gap and the reaction time of the system automatic control(i.e. the speed at which this force must be changed when it encounters a disturbance). The physical dimensions of the electronic system do not have a direct relationship with the weight of the machine's rotor; they are most likely related to the ratio of the indicator between the magnitude of the interference and the weight of the rotor. Therefore, a small shell will be sufficient for a large mechanism equipped with a relatively heavy rotor subject to little disturbance. At the same time, a mechanism subject to greater interference must be equipped with a large electrical cabinet.

2. Some characteristics of AMP

Air gap

The air gap is the space between the rotor and stator. The amount of gap indicated e, depends on diameter D rotor or bearing.

As a rule, the following values ​​are usually used:

D (mm)	e(mm)
< 100	0,3 - 0,6
100 - 1 000	0,6 - 1,0

Rotational speed

The maximum rotation speed of a radial magnetic bearing depends only on the characteristics of the electromagnetic rotor plates, namely the resistance of the plates to centrifugal force. When using standard inserts, peripheral speeds of up to 200 m/s can be achieved. The rotation speed of the axial magnetic bearing is limited by the resistance of the cast steel thrust disk. A peripheral speed of 350 m/s can be achieved using standard equipment.

The AMP load depends on the ferromagnetic material used, the rotor diameter and the longitudinal length of the suspension stator. Maximum specific load of AMP made from standard material, is 0.9 N/cm². This maximum load is smaller compared to the corresponding values ​​of classical bearings, however, the high permissible peripheral speed allows the shaft diameter to be increased so as to obtain the largest possible contact surface and therefore the same load limit as for a classical bearing without the need to increase its length.

Power consumption

Active magnetic bearings have very low energy consumption. This energy consumption comes from losses due to hysteresis, eddy currents (Foucault currents) in the bearing (power taken from the shaft) and heat losses in the electronic shell. AMPs consume 10-100 times less energy than classic mechanisms of comparable sizes. Power consumption electronic system control, which requires an external current source, is also very low. Batteries are used to maintain the operating condition of the gimbal in the event of a network failure - in this case they turn on automatically.

Ambient conditions

AMPs can be installed directly in the operating environment, completely eliminating the need for appropriate couplings and devices, as well as barriers for thermal insulation. Today, active magnetic bearings operate in the most various conditions: vacuum, air, helium, hydrocarbon, oxygen, sea ​​water and uranium hexafluoride, as well as at temperatures from - 253° From to + 450 ° WITH.

3. Advantages of magnetic bearings

• Non-contact/liquidless
  - absence of mechanical friction
  - no oil
  - increased peripheral speed
  
• Increased reliability
  - operational reliability of the control cabinet > 52,000 hours.
  - operational reliability of EM bearings > 200,000 hours.
  - almost complete lack of preventative maintenance
  
• Smaller turbomachinery dimensions
  - lack of lubrication system
  - smaller dimensions (P = K*L*D²*N)
  - less weight
  
• Monitoring
  - bearing load
  - turbomachine load
• Adjustable Parameters
  - active magnetic bearing control system
  - rigidity (varies depending on the dynamics of the rotor)
  - damping (varies depending on the dynamics of the rotor)
  
• Sealless operation (compressor and drive in one housing)
  - bearings in process gas
  - wide operating temperature range
  - optimization of rotor dynamics by shortening it

The undeniable advantage of magnetic bearings is the complete absence of rubbing surfaces, and, consequently, wear, friction, and most importantly the absence of departure from working area particles generated during the operation of conventional bearings.

Active magnetic bearings are characterized by high load capacity and mechanical strength. They can be used when high speeds rotation, as well as in airless space and at different temperatures.

Materials provided by “S2M” company, France ( www.s2m.fr).

Below we consider the design of Nikolaev’s magnetic suspension, who argued that it is possible to ensure levitation of a permanent magnet without a stop. An experiment is shown to test the operation of this circuit.

The neodymium magnets themselves are sold in this Chinese store.

Magnetic levitation without energy consumption - fantasy or reality? Is it possible to make a simple magnetic bearing? And what did Nikolaev actually show in the early 90s? Let's look at these questions. Anyone who has ever held a pair of magnets in their hands has probably wondered: “Why can’t I make one magnet float above the other without outside support? Possessing such a unique as a constant magnetic field, they are repelled by poles of the same name completely without energy consumption. This is an excellent basis for technical creativity! But it's not that simple.

Back in the 19th century, the British scientist Earnshaw proved that using only permanent magnets, it is impossible to stably hold a levitating object in a gravitational field. Partial levitation, or, in other words, pseudo-levitation, is possible only with mechanical support.

How to make a magnetic suspension?

A simple magnetic suspension can be made in a couple of minutes. You will need 4 magnets at the base to make a support base, and a pair of magnets attached to the levitating object itself, which can be, for example, a felt-tip pen. Thus, we got a floating structure with an unstable balance on both sides of the felt-tip pen axis. A regular mechanical stop will help stabilize the position.

The simplest magnetic suspension with a stop

This design can be configured in such a way that the main weight of the levitating object rests on the support magnets, and the lateral thrust force is so small that the mechanical friction there practically approaches zero.

Now it would be logical to try to replace the mechanical stop with a magnetic one in order to achieve absolute magnetic levitation. But, unfortunately, this cannot be done. Perhaps it is due to the primitiveness of the design.

Alternative design.

Let's consider more reliable system such a suspension. Ring magnets are used as a stator, through which the axis of rotation of the bearing passes. It turns out that at a certain point, ring magnets have the property of stabilizing other magnets along their magnetization axis. But the rest is the same. There is no stable equilibrium along the axis of rotation. This has to be eliminated with an adjustable stop.

Let's consider a more rigid structure.

Perhaps here it will be possible to stabilize the axis using a persistent magnet. But even here it was not possible to achieve stabilization. It may be necessary to place thrust magnets on both sides of the bearing's axis of rotation. A video with Nikolaev’s magnetic bearing has been discussed on the Internet for a long time. The image quality does not allow us to examine this design in detail and it seems that he managed to achieve stable levitation solely with the help of permanent magnets. In this case, the device diagram is identical to that shown above. Only a second magnetic stop has been added.

Checking the design of Gennady Nikolaev.

First, watch the full video, which shows Nikolaev's magnetic suspension. This video forced hundreds of enthusiasts in Russia and abroad to try to make a structure that could create levitation without a stop. But, unfortunately, at present no working design of such a suspension has been created. This casts doubt on Nikolaev’s model.

For testing, exactly the same design was made. In addition to all the additions, the same ferrite magnets as Nikolaev’s were supplied. They are weaker than neodymium ones and do not push out with such enormous force. But testing in a series of experiments brought only disappointment. Unfortunately, this scheme also turned out to be unstable.

Conclusion.

The problem is that ring magnets, no matter how strong they are, are not able to keep the bearing axis in balance with the force from the side thrust magnets that is necessary for its lateral stabilization. The axle simply slides to the side at the slightest movement. In other words, the force with which the ring magnets stabilize the axis within themselves will always be less strength necessary to stabilize the axis in the lateral direction.

So what did Nikolaev show? If you look at this video more carefully, you suspect that due to the poor quality of the video, the needle stop is simply not visible. Is it by chance that Nikolaev tries to demonstrate the most interesting things? The very possibility of absolute levitation on permanent magnets, the law of conservation of energy is not violated here. Perhaps they have not yet created a form of magnet that will create the necessary potential well that reliably holds a bunch of other magnets in stable equilibrium.

Below is a diagram of the magnetic suspension

Drawing of a magnetic suspension with permanent magnets

after watching videos of certain comrades, like these

I decided and I will check in on this topic. In my opinion, the video is quite illiterate, so it’s quite possible to whistle from the stalls.

After going through a bunch of diagrams in my head, looking at the principle of suspension in the central part in Beletsky’s video, understanding how the Levitnon toy works, I came up with a simple diagram. It is clear that there should be two supporting spikes on one axis, the spike itself is made of steel, and the rings are rigidly fixed on the axis. Instead of solid rings, it is quite possible to place not very large magnets in the shape of a prism or cylinder located around the circumference. The principle is the same as in the famous toy "Livitron". only instead of a geroscopic moment that prevents the top from tipping over, we use a “thrust” between supports rigidly fixed to the axis.

Below is a video with the toy "Livitron"

and here is the diagram that I propose. in fact, this is the toy in the video above, but as I already said, it needs something that would prevent the support spike from tipping over. In the video above, the gyroscopic moment is used, I use two stands and a spacer between them.

Let's try to justify the work of this design, as I see it:

the magnets are pushed away, which means there is a weak point - you need to stabilize these spikes along the axis. here I used the following idea: the magnet tries to push the spike into the area with the lowest field strength, because the spike has a magnetization opposite to the ring and the magnet itself is ring-shaped, where in sufficient large area located along the axis, the tension is less than at the periphery. those. The distribution of magnetic field intensity in shape resembles a glass - the intensity is maximum in the wall, and minimum on the axis.

the spike must be stabilized along the axis, while simultaneously being pushed out of the ring magnet into the area with the lowest field strength. those. if there are two such spikes on one axis and the ring magnets are rigidly fixed, the axis should “freeze”.

it turns out that being in a zone with lower field strength is the most energetically favorable.

Having rummaged around on the Internet I found a similar design:

here, too, a zone with lower tension is formed, it is also located along the axis between the magnets, and the angle is also used. In general, the ideology is very similar, but if we talk about a compact bearing, the option above looks better, but requires specially shaped magnets. those. The difference between the schemes is that I squeeze the supporting part into a zone with less tension, and in the scheme above, the very formation of such a zone ensures the position on the axis.
To make the comparison clearer, I redrawn my diagram:

They are essentially mirror images. In general, the idea is not new - they all revolve around the same thing, I even have suspicions that the author of the video above simply did not look for the proposed solutions

here it’s almost one to one, if the conical stops are made not solid, but composite - magnetic core + ring magnet, then you’ll get my circuit. I would even say the initial unoptimized idea - the picture below. only the picture above works to “attract” the rotor, but I initially planned “repulsion”


For those who are especially gifted, I want to note that this suspension does not violate Earnshaw’s theorem (prohibition). The fact is that we're talking about This is not about a purely magnetic suspension, without rigidly fixing the centers on the axis, i.e. one axis is rigidly fixed, nothing will work. those. It's about choosing a fulcrum and nothing more.

in fact, if you watch Beletsky’s video, you can see that approximately the same configuration of fields is already used in some places, only the final touch is missing. the conical magnetic circuit distributes the “repulsion” along two axes, but Earnshaw ordered the third axis to be fixed differently, I did not argue and fixed it rigidly mechanically. I don’t know why Beletsky didn’t try this option. in fact, he needs two “livitrons” - the supports are fixed on the axis, and connected to the tops with a copper tube.

You can also note that you can use tips from any sufficiently strong diamegnetic material in place of a magnet with a polarity opposite to the magnetic support ring. those. replace the combination of magnet + conical magnetic circuit, simply with a cone made of diamagnetic material. fixation on the axis will be more reliable, but diamagnets are not characterized by strong interaction and high field strengths and a large “volume” of this field are needed in order to apply this in any way. Due to the fact that the field is axially uniform relative to the axis of rotation, changes in the magnetic field will not occur during rotation, i.e. such a bearing does not create resistance to rotation.

According to the logic of things, this principle should also be applicable for plasma suspension - a patched “magnetic bottle” (corktron), so wait and see.

Why am I so confident in the result? well, because it cannot help but exist :) the only thing that is possible is to make magnetic cores in the shape of a cone and a cup for a more “hard” field configuration.
Well, you can also find a video with a similar suspension:

here the author does not use any magnetic circuits and uses a focus on the needle, as is generally necessary, understanding Earnshaw’s theorem. but the rings are already rigidly fixed to the axis, which means you can spread the axis between them, which can be easily achieved using conical magnetic cores on magnets on the axis. those. Until the “bottom” of the “magnetic cup” is penetrated, it becomes increasingly difficult to push the magnetic circuit into the ring because the magnetic permeability of air is less than that of the magnetic circuit - a decrease in the air gap will lead to an increase in field strength. those. one axis is rigidly fixed mechanically - then there will be no need for support on the needle. those. see the very first picture.

P.S.
Here's what I found. from the series, the bad head won’t let go of his hands yet - the author is still Beletsky - it’s screwed up there, mother, don’t worry - the configuration of the field is quite complex, moreover, it is not uniform along the axis of rotation, i.e. when rotating, there will be a change in the magnetic induction in the axis with all the sticking out... pay attention to the ball in the ring magnet, on the other hand there is a cylinder in the ring magnet. those. the person stupidly ruined the principle of suspension described here.

Well, or soldered the suspension in the photo, i.e. the peppers in the photo use a support for the needle, and he hung a ball in place of the needle - oh shaitan - it worked - who would have thought (I remember they proved to me that I did not understand Earnshaw's theorem correctly), but hanging two balls and using only two rings apparently is not smart enough. those. the number of magnets in the device in the video can easily be reduced to 4, and possibly to 3, i.e. a configuration with a cylinder in one ring and a ball in the other can be considered experimentally proven to work, see the picture of the original idea. there I used two simitric stops and a cylinder + cone, although I think that the cone and part of the sphere from the pole to the diameter work the same.

therefore, the stop itself looks like this - it’s a magnetic circuit (i.e. iron, nickel, etc.) it’s just

a ring magnet is installed. the counter part is the same, only in reverse :) and two stops in the spacer work - comrade Earnshaw forbade working on one stop.

Many bearing consumers believe magnetic bearings a kind of “black box”, although they have been used in industry for quite a long time. They are usually used in transportation or preparation natural gas, in the processes of its liquefaction and so on. They are often used by floating gas processing complexes.

Magnetic bearings operate by magnetic levitation. They work thanks to the forces generated by the magnetic field. In this case, the surfaces do not contact each other, so there is no need for lubrication. This type bearings are able to function even in rather harsh conditions, namely at cryogenic temperatures, extreme pressures, high speeds, and so on. At the same time, magnetic bearings show high reliability.

The radial bearing rotor, which is equipped with ferromagnetic plates, is held in the desired position with the help of magnetic fields created by electromagnets placed on the stator. The functioning of axial bearings is based on the same principles. In this case, opposite the electromagnets on the rotor, there is a disk that is mounted perpendicular to the axis of rotation. The rotor position is monitored by induction sensors. These sensors quickly detect all deviations from the nominal position, as a result of which they create signals that control currents in the magnets. These manipulations allow you to hold the rotor in the desired position.

Advantages of magnetic bearings undeniable: they do not require lubrication, do not threaten environment, consume little energy and, due to the absence of contacting and rubbing parts, operate for a long time. In addition, magnetic bearings have low vibration levels. Today there are models with a built-in monitoring and condition control system. At the moment, magnetic bearings are mainly used in turbochargers and compressors for natural gas, hydrogen and air, in cryogenic technology, in refrigeration units, in turboexpanders, in vacuum technology, in electric generators, in control and measuring equipment, in high-speed polishing, milling and grinding machines.

The main disadvantage of magnetic bearings- dependence on magnetic fields. The disappearance of the field can lead to catastrophic failure of the system, so they are often used with safety bearings. Typically, they are used as rolling bearings that can withstand two or one failure of magnetic models, after which their immediate replacement is required. Also for magnetic bearings, bulky and complex systems controls that significantly complicate the operation and repair of the bearing. For example, to control these bearings, they often install special cabinet management. This cabinet is a controller that interacts with magnetic bearings. With its help, a current is supplied to the electromagnets, which regulates the position of the rotor, guarantees its non-contact rotation and maintains its stable position. In addition, during the operation of magnetic bearings, the problem of heating the winding of this part may arise, which occurs due to the passage of current. Therefore, additional cooling systems are sometimes installed with some magnetic bearings.

One of the largest manufacturers of magnetic bearings- S2M company, which participated in the development of the complete life cycle magnetic bearings as well as permanent magnet motors: from development to commissioning, production and practical solutions. S2M has always been committed to an innovative policy aimed at simplifying bearing designs to reduce costs. She tried to make magnetic models more accessible for wider use by the industrial consumer market. Companies producing various compressors and vacuum pumps have collaborated with S2M, mainly for oil and gas industry. At one time, the network of S2M services spread throughout the world. Its offices were in Russia, China, Canada and Japan. In 2007, S2M was acquired by the SKF group for fifty-five million euros. Today, magnetic bearings using their technologies are manufactured by the manufacturing division of A&MC Magnetic Systems.

Compact and cost-effective modular systems equipped with magnetic bearings are increasingly used in industry. Compared to usual traditional technologies they have many advantages. Thanks to miniaturized innovative motor/bearing systems, the integration of such systems into modern series products has become possible. They are used today in high-tech industries (semiconductor production). Recent inventions and developments in the field of magnetic bearings are clearly aimed at maximizing the structural simplification of this product. This is to reduce bearing costs, making them more accessible to the wider industrial market that clearly needs such innovation.

In a variety of modern electromechanical products and technical products, the magnetic bearing is the main component that determines the technical and economic characteristics and increases trouble-free operational period. Compared to traditional bearings, magnetic bearings completely eliminate the friction force between stationary and moving parts. The presence of this property makes it possible to implement increased speeds in designs magnetic systems. Magnetic bearings are made of high-temperature superconducting materials, which rationally influence their properties. These properties include a significant reduction in costs for model designs cooling systems and such important parameter, as long-term maintenance of a magnetic bearing in working condition.

Operating principle of magnetic suspensions

The operating principle of magnetic suspensions is based on the use of free levitation, which is created by magnetic and electric fields. A rotating shaft using such suspensions, without the use of physical contact, is literally suspended in a powerful magnetic field. Its relative revolutions pass without friction and wear, while achieving highest reliability. The fundamental component of a magnetic suspension is the magnetic system. Its main purpose is to create a magnetic field of the required shape, providing the required traction characteristics in work area at a certain control displacement of the rotor and the rigidity of the bearing itself. Such parameters of magnetic bearings are directly dependent on the design of the magnetic system, which must be developed and calculated based on its weight and size component - an expensive cryogenic cooling system. What the electromagnetic field of magnetic suspensions are capable of can be clearly seen in the operation of the children's toy Levitron. In practice, magnetic and electric suspensions exist in nine types, differing in their operating principle:

• magnetic and hydrodynamic suspensions;
• suspensions operating on permanent magnets;
• active magnetic bearings;
• conditioning hangers;
• LC - resonant types of suspensions;
• induction bearings;
• diamagnetic types of suspensions;
• superconducting bearings;
• electrostatic suspensions.

If we test all these types of suspensions in terms of popularity, then in the current realities, active magnetic bearings (AMP) have taken the leading position. In appearance, they represent a mechatronic device system in which the stable state of the rotor is achieved by the forces of magnetic attraction present. These forces act on the rotor from the side of the electromagnets, electricity in which it is adjusted by an automatic control system based on sensor signals from the electronic control unit. Such control units can use either a traditional analogue or a more innovative digital signal processing system. Active magnetic bearings have excellent dynamic characteristics, reliability and high efficiency. Unique features active magnetic bearings contribute to their widespread adoption. AMPs are effectively used, for example, in the following equipment:
- gas turbine units;
- high-speed rotor systems;
- electric motors;
- turboexpanders;
- inertial energy storage devices, etc.
While active magnetic bearings require external source current and expensive and complex control equipment. At the moment, AMP developers are conducting active work to create a passive type of magnetic bearings.